Good to have your new company, Applewine. There is a hitch with this proposal, though. Point-of-sale for Amazon treebooks is the USA and they're available to anyone anywhere. Point-of-sale of an ebook is the location of the computer used for download. This means that geographical restrictions come into play.
Many agents and agents, you see, optimise income and royalty advances by often selling the same title to different publishers in different countries so that an ebook title that might be legally downloadable in, say, the USA cannot be legally downloaded in any other country where another publishing company holds territorial rights.
My own independent house holds international print and digital rights on all our titles and we do not use Agency 5 or DRM, so offering treebook and ebook as a package at Amazon would be just dandy by us. Other publishers, though, are legally restricted by their author/agent agreements as well as in-store pricing anomalies.